# This shows how regsub can explain itself
tcl>regsub -all -- {(a+)b} {abracaadabraaa!} {<[ \&='&', \\1='\1', \\2='\2' ]>}
<[ &='ab', \1='a', \2='' ]>racaad<[ &='ab', \1='a', \2='' ]>raaa!